Multilayer structure and process for producing the same

ABSTRACT

A multilayer structure having a layer of an adhesive resin composition (A) and a layer of another resin (B), wherein the adhesive resin composition (A) includes a thermoplastic resin (a1) containing functional groups of at least one kind selected from the group consisting of a boronic acid group and boron-containing groups capable of being converted into a boronic acid group in the presence of water, and a polyolefin (a2) which does not contain the functional groups, the blending weight ratio (a1/a2) of the thermoplastic resin (a1) to the polyolefin (a2) is 1/99 to 15/85, and particles of the thermoplastic resin (a1) are dispersed with an average particle diameter of 0.1 to 1.2 μm in a matrix of the polyolefin (a2). Consequently, a multilayer structures having satisfactory interlayer adhesion strength can be provided even if the content of the resin having a special functional group in the adhesive resin composition layer is reduced.

TECHNICAL FIELD

The present invention relates to a multilayer structure having a layerof an adhesive resin composition and a layer of another resin, and to amethod for producing the same.

BACKGROUND ART

Ethylene-vinyl alcohol copolymers (hereinafter, sometimes abbreviated asEVOH) are excellent in, for example, gas barrier properties, oilresistance and aroma retention properties and therefore have been usedin various applications. However, EVOH also has some drawbacks of highmoisture permeability and high expense. In order to maintain advantagesinherent in EVOH and compensate defects thereof, EVOH is usually used inlamination with a thermoplastic resin, such as polyolefin andpolystyrene. However, because the adhesion of EVOH to such athermoplastic resin is poor, it is necessary to form an adhesive layerbetween both layers. As such an adhesive, modified polyolefins, such aspolyolefins (e.g., polyethylene, polypropylene, and ethylene-vinylacetate copolymers) modified with maleic anhydride and ethylene-ethylacrylate-maleic anhydride copolymers are used widely. However, when suchan adhesive is used, adhesion may be insufficient, depending on thebrand of EVOH. In some cases, the interlayer adhesion strength aftercoextrusion molding may change with time. On the other hand, since aresin containing functional groups of at least one kind selected fromthe group consisting of a boronic acid group and boron-containing groupseach capable of being converted into a boronic acid group in thepresence of water has a very high reactivity with EVOH, it is possibleto solve the aforementioned problems by using it as an adhesive.

WO 02/060961, which is also published as EP1369438A, discloses amultilayer structure produced by laminating an EVOH layer and apolyolefin layer via a layer of an adhesive. As the adhesive, a resincomposition containing a polyolefin and a styrene-hydrogenated dieneblock copolymer containing in its side chain at least one functionalgroup selected from the group consisting of a boronic acid group andboron-containing groups each capable of being converted into a boronicacid group in the presence of water is used. It is shown that multilayerstructures obtained in such a procedure have satisfactory interlayeradhesion. It is disclosed that the adhesive resin composition usedtherein can be produced by melt-kneading the styrene-hydrogenated dieneblock copolymer and the polyolefin using a Banbury mixer, a twin screwextruder, or the like. In Examples of the publication cited above, amultilayer structure is produced by melt-kneading thestyrene-hydrogenated diene block copolymer and the polyolefin using atwin screw extruder to obtain an adhesive resin composition, and thenfeeding the resulting adhesive resin composition, a polyolefin and anEVOH into single screw extruders, respectively, followed by coextrusionmolding.

Since a resin containing functional groups of at least one kind selectedfrom the group consisting of a boronic acid group and boron-containinggroups each capable of being converted into a boronic acid group in thepresence of water is expensive, it is preferable, from the economicalpoint of view, to use it by diluting it with an inexpensive polyolefinas disclosed in the publication cited above. However, the interlayeradhesion is not sufficient in some applications and, therefore, there isa strong demand for obtaining multilayer structures having satisfactoryinterlayer adhesion strength even if the used amount of the resin havinga special functional group is reduced.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The present invention was made in order to solve the aforementionedproblems. An object of the present invention is to provide a multilayerstructures having satisfactory interlayer adhesion strength even if thecontent of the resin having a special functional group in the adhesiveresin composition layer is reduced. Another object is to providesuitable methods for producing such multilayer structures.

Means for Solving the Problem

The aforementioned problems are solved by providing a multilayerstructure having a layer of an adhesive resin composition (A) and alayer of another resin (B), wherein the adhesive resin composition (A)comprises a thermoplastic resin (a1) containing functional groups of atleast one kind selected from the group consisting of a boronic acidgroup and boron-containing groups capable of being converted into aboronic acid group in the presence of water, and a polyolefin (a2) whichdoes not contain the functional groups, the blending weight ratio(a1/a2) of the thermoplastic resin (a1) to the polyolefin (a2) is 1/99to 15/85, and particles of the thermoplastic resin (a1) are dispersedwith an average particle diameter of 0.1 to 1.2 μm in a matrix of thepolyolefin (a2).

In this embodiment, it is preferable that the melt flow rate (at 190° C.under a load of 2160 g) of the thermoplastic resin (a1) is from 0.7 to 4g/10 min and also that the melt flow rate (at 190° C. under a load of2160 g) of the polyolefin (a2) is from 0.1 to 10 g/10 min. It is onepreferred embodiment that the resin (B) is an ethylene-vinyl alcoholcopolymer (B1). In this embodiment, a layer of the ethylene-vinylalcohol copolymer (B1) and a layer of a polyolefin (B2) are preferablylaminated to each other via the layer of the adhesive resin composition(A).

The aforementioned problems are solved also by providing a method forproducing the multilayer structure, the method including providing acoextrusion molding machine equipped with a plurality of extruders,feeding pellets of the thermoplastic resin (a1) and pellets of thepolyolefin (a2) to one extruder, feeding pellets of the resin (B) toanother extruder, and performing coextrusion molding. In thisembodiment, the pellets of the thermoplastic resin (a1) and the pelletsof the polyolefin (a2) are preferably dry blended in advance, and thenfed to the extruder. The extruder to which the pellets of thethermoplastic resin (a1) and the pellets of the polyolefin (a2) are fedis also preferably a single screw extruder. The linear velocity of ascrew periphery in the single screw extruder is more preferably from 0.8to 8 m/min.

Effect of the Invention

Multilayer structures of the present invention have satisfactoryinterlayer adhesion strength even at a reduced content of the resinhaving a special functional group in the adhesive resin compositionlayer. As a result, it is possible to provide multilayer structureshaving satisfactory interlayer adhesion at low costs. By the use ofproduction methods of the present invention, it is possible to obtainsuch multilayer structures easily.

BEST MODE FOR CARRYING OUT THE INVENTION

The adhesive resin composition (A) used in the multilayer structures ofthe present invention is a composition having a thermoplastic resin (a1)containing functional groups of at least one kind selected from thegroup consisting of a boronic acid group and boron-containing groupscapable of being converted into a boronic acid group in the presence ofwater, which are hereinafter occasionally referred to asboron-containing functional groups, and a polyolefin (a2) which does notcontain the functional groups.

First, the thermoplastic resin (a1) is described. The thermoplasticresin (a1) is characterized by containing functional groups of at leastone kind selected from the group consisting of a boronic acid group andboron-containing groups capable of being converted into a boronic acidgroup in the presence of water. Among the boron-containing functionalgroups, the boronic acid group is a group represented by the followingformula (I).

The boron-containing group capable of being converted into a boronicacid group in the presence of water indicates a boron-containing groupthat can be hydrolyzed in the presence of water to be converted into aboronic acid group represented by the above formula (I). Morespecifically, the above boron-containing group means a functional groupcapable of being converted into a boronic acid group when beinghydrolyzed under conditions of from room temperature to 150° C. for from10 minutes to 2 hours by use, as a solvent, of water only, a mixture ofwater and an organic solvent (e.g., toluene, xylene and acetone), amixture of a 5% aqueous boric acid solution and the above describedorganic solvent, or the like. Representative examples of such functionalgroups include boronic ester groups represented by the following generalformula (II), boronic anhydride groups represented by the followinggeneral formula (III), and boronic acid salt groups represented by thefollowing general formula (IV):

wherein X₁ and X₂ are the same or different and each represent ahydrogen atom, an aliphatic hydrocarbon group (e.g., a linear orbranched alkyl or alkenyl group having from 1 to 20 carbon atoms), analicyclic hydrocarbon group (e.g., a cycloalkyl group and a cycloalkenylgroup), or an aromatic hydrocarbon group (e.g., phenyl group andbiphenyl group), where the aliphatic hydrocarbon group, the alicyclichydrocarbon group and the aromatic hydrocarbon group may have asubstituent, X₁ and X₂ may be combined together, provided that in nocases both X₁ and X₂ are hydrogen atoms; R₁, R₂ and R₃ each represent ahydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbongroup or an aromatic hydrocarbon group like X₁ and X₂ mentioned above,and M represents alkali metal.

Specific examples of the boronic ester group represented by generalformula (II) include dimethyl boronate group, diethyl boronate group,dipropyl boronate group, diisopropyl boronate group, dibutyl boronategroup, dihexyl boronate group, dicyclohexyl boronate group, ethyleneglycol boronate group, propylene glycol boronate group, 1,3-propanediolboronate group, 1,3-butanediol boronate group, neopentyl glycol boronategroup, catechol boronate group, glycerin boronate group,trimethylolethane boronate group, trimethylolpropane boronate group,diethanolamine boronate group, and the like.

The boronic acid salt groups represented by the general formula (IV) maybe alkali metal boronate groups, etc. Specific examples include sodiumboronate group, potassium boronate group, and the like.

Among such boron-containing functional groups, cyclic boronate estergroups are preferred in view of thermal stability. Examples of thecyclic boronate ester groups include 5-membered or 6-memberedring-containing cyclic boronate ester groups. Specific examples includeethylene glycol boronate group, propylene glycol boronate group,1,3-propanediol boronate group, 1,3-butanediol boronate group, glycerinboronate group, and the like.

The thermoplastic resin (a1) may contain only one kind of or two or morekinds of boron-containing functional groups. The amount of theboron-containing functional groups is preferably from 0.0001 to 0.002equivalents per gram of the thermoplastic resin (a1), namely from 100 to2000 μeq/g, and more preferably from 150 to 1500 μeq/g. When the amountof the functional groups is less than 100 μeq/g, the interlayer adhesionstrength of the resulting multilayer structure may deteriorate. When theamount of the functional groups exceeds 2000 μeq/g, gellation easilyoccurs and the appearance of the resulting multilayer structure maydeteriorate.

Although the bonding form of the boron-containing functional groupscontained in the thermoplastic resin (a1) of the present invention isnot particularly restricted, the boron-containing functional groups arepreferably contained as side chains of the polymer. It is easy to obtaina large content of boron-containing functional groups when they arecontained as side chains.

When the boron-containing functional groups are bonded only to terminalsof a polymer, the amount of the functional groups becomes relatively lowparticularly in a polymer of high molecular weight, and the reactivityof the thermoplastic resin (a1) may become insufficient. Theboron-containing functional groups may be contained at side chains andterminals.

Specific examples of the thermoplastic resin (a1) include polyolefinssuch as polyethylene (very low density, low density, middle density,high density), ethylene-vinyl acetate copolymers, ethylene-acrylic estercopolymers, polypropylene, ethylene-propylene copolymers and copolymersof ethylene with an α-olefin such as 1-butene, isobutene,3-methylpentene, 1-hexene and 1-octene; products resulting from graftmodification of the aforementioned polyolefins with maleic anhydride,glycidyl methacrylate and the like; styrene resins such as polystyreneand styrene-acrylonitrile copolymers; styrene-diene block copolymerssuch as styrene-butadiene block copolymers, styrene-isoprene copolymers,styrene-butadiene-styrene block copolymers and styrene-isoprene-styreneblock copolymers; styrene-hydrogenated diene block copolymers such asstyrene-hydrogenated butadiene block copolymers, styrene-hydrogenatedisoprene copolymers, styrene-hydrogenated butadiene-styrene blockcopolymers and styrene-hydrogenated isoprene-styrene block copolymers;(meth) acrylic ester resins such as poly (methyl acrylate), poly (ethylacrylate) and poly (methyl methacrylate); vinyl halide-based resins suchas poly (vinyl chloride) and vinylidene fluoride; semiaromaticpolyesters such as poly (ethylene terephthalate) and poly (butyleneterephthalate); and aliphatic polyesters such as polyvalerolactone,polycaprolactone, poly (ethylene succinate) and poly (butylenesuccinate). These may be used singly or in combination of two or morekinds. Among these, polyolefins and styrene-hydrogenated diene blockcopolymers are preferable, and styrene-hydrogenated diene blockcopolymers are particularly preferable.

When the thermoplastic resin (a1) is a styrene-hydrogenated diene blockcopolymer, the weight ratio of styrene units to hydrogenated diene unitscontained in the copolymer resin is preferably from 5/95 to 70/30, andmore preferably from 10/90 to 50/50. When the weight ratio is withinsuch ranges, the compatibility of the thermoplastic resin (a1) with thepolyolefin (a2) becomes suitable, and the average particle diameter ofthe thermoplastic resin (a1) easily falls into a preferred range. When ahigh interlayer adhesion strength is particularly desired, a smallercontent of styrene units is preferred. Specifically, the weight ratio ofstyrene units to hydrogenation diene units is preferably 30/70 or less.

The melt flow rate (at 190° C., under a load of 2160 g) of thethermoplastic resin (a1) is preferably from 0.7 to 4 g/10 min. When themelt flow rate is included in this range, the average particle diameterof the thermoplastic resin (a1) dispersing in the adhesive resincomposition (A) easily falls into a preferred range. The melt flow rateis more preferably 1 g/10 min or more, and even more preferably 1.5 g/10min or more. The melt flow rate is more preferably 3 g/10 min or less,and even more preferably 2.5 g/10 min or less.

Next, a representative method for producing the thermoplastic resin (a1)containing a boron-containing functional group for use in the presentinvention is described.

First method: the thermoplastic resin (a1) containing boron-containingfunctional groups is obtained by causing a boran complex and a trialkylborate to react with a thermoplastic resin having an olefinic doublebond under a nitrogen atmosphere to produce a thermoplastic resincontaining a dialkyl boronate group and then, if necessary, causingwater or alcohols to react. In this way, a boron-containing functionalgroup is introduced to the olefinic double bond of the thermoplasticresin by addition reaction.

An olefinic double bond is introduced, for example, to an end bydisproportionation occurring at the time of termination of radicalpolymerization or into a main chain or a side chain by a side reactionoccurring during polymerization. In particular, the aforementionedpolyolefin is preferred because it is possible to introduce the olefinicdouble bond thereto easily by thermal decomposition under oxygen-freeconditions or copolymerization of diene compounds. Styrene-hydrogenateddiene block copolymers are preferred because it is possible to cause anolefinic double bond to remain moderately by controlling a hydrogenationreaction.

The content of double bonds in the thermoplastic resin used as a rawmaterial is preferably from 100 to 2000 μeq/g, and more preferably from200 to 1000 μeq/g. The use of such a raw material makes it easy tocontrol the amount of boron-containing functional groups introducedthereto. It will also become possible at the same time to control theamount of olefinic double bonds remaining after the introduction offunctional groups.

Preferred examples of the borane complex include borane-tetrahydrofurancomplex, borane-dimethylsulfide complex, borane-pyridine complex,borane-trimethylamine complex, borane-triethylamine complex, and thelike. Among these, borane-dimethylsulfide complex, borane-trimethylaminecomplex and borane-triethylamine complex are more preferable. The amountof the borane complex to be supplied is preferably within the range offrom 1/3 equivalents to 10 equivalents to the olefinic double bonds ofthe thermoplastic resin.

Preferred examples of the trialkyl borates include lower alkyl esters ofboric acid such as trimethyl borate, triethyl borate, tripropyl borateand tributyl borate. The amount of the trialkyl borate to be supplied ispreferably within the range of from 1 to 100 equivalents to the olefinicdouble bonds of the thermoplastic resin. There is no need to use asolvent, but when use it, a saturated hydrocarbon solvent, such ashexane, heptane, octane, decane, dodecane, cyclohexane, ethylcyclohexaneand decalin, is preferred. The reaction temperature is typically withinthe range of from room temperature to 300° C., and preferably from 100to 250° C. It is recommended to carry out a reaction at a temperaturewithin such ranges for 1 minute to 10 hours, preferably for 5 minutes to5 hours.

The dialkyl boronate group introduced to a thermoplastic resin throughthe above described reaction can be hydrolyzed to form a boronic acidgroup by a known method. It is also allowed to undergotransesterification with an alcohol by a known method to form a boronategroup. Further, it can be allowed to undergo dehydration condensation byheating to form a boronic anhydride group. Furthermore, it can beallowed to react with a metal hydroxide or a metal alcoholate to form aboronic acid salt group.

Such conversion of a boron-containing functional group is typicallycarried out using an organic solvent such as toluene, xylene, acetoneand ethyl acetate. Examples of the alcohols include monoalcohols such asmethanol, ethanol and butanol; and polyhydric alcohols such as ethyleneglycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, neopentylglycol, glycerin, trimethylolmethane, pentaerythritol anddipentaerythritol. Examples of the metal hydroxide include hydroxides ofalkali metals such as sodium and potassium. Examples of the metalalcoholate include those made of the above described metals and theabove described alcohols. These are not limited to those listed asexamples. The amounts of these reagents to be used are typically from 1to 100 equivalents to the dialkyl boronate groups.

Second method: the thermoplastic resin (a1) containing boron-containingfunctional groups is obtained by performing an amidation reaction of aknown thermoplastic resin containing a carboxyl group and an aminogroup-containing boronic acid or an amino group-containing boronic acidester such as m-aminophenylbenzene boronic acid and m-aminophenylboronicacid ethylene glycol ester using a known method. In this method, acondensing agent such as carbodiimide may be employed. Theboron-containing functional group introduced into the thermoplasticresin in such a way can be converted into another boron-containingfunctional group by the method described above.

Examples of the thermoplastic resin containing a carboxyl group include,but are not restricted to, resins having a carboxyl group on their ends,such as semiaromatic polyester and aliphatic polyester; resins resultingfrom introduction of monomer units having a carboxyl group such asacrylic acid, methacrylic acid and maleic anhydride to polyolefin,styrene-based resin, (meth)acrylic acid ester-based resin, vinylhalide-based resin, or the like, by copolymerization; and resinsresulting from introduction of maleic anhydride, or the like, into theaforementioned thermoplastic resin containing an olefinic double bond byan addition reaction.

The polyolefin (a2) which constitutes the adhesive resin composition (A)is a polyolefin which does not contain the boron-containing functionalgroups. Specific examples thereof include polyethylene (very lowdensity, low density, middle density, high density), ethylene-vinylacetate copolymers, polypropylene and ethylene-propylene copolymers. Itis also permitted to use products resulting from graft modification ofpolyolefins with maleic anhydride, glycidyl methacrylate, or the like.Among these, it is preferable to use an ethylene-based resin.Particularly from the interlayer adhesion point of view, an ethyleneresins having a low crystallization rate is suitably used. Preferableexamples of the ethylene-based resin having a low crystallization rateinclude polyethylene having a density of from 0.912 to 0.935 g/cm³. Thedensity is more preferably 0.930 g/cm³ or less. Examples of suchpolyethylene include very low density polyethylene and low densitypolyethylene (including LLDPE). It is also permitted to adjust thedensity to that shown above by mixing plural kinds of polyethylene.Other preferable examples of the ethylene-based resin having a lowcrystallization rate include ethylene-vinyl acetate copolymers, thedensity of which is preferably from 0.94 to 0.98 g/cm³, and morepreferably 0.96 g/cm³ or less. A mixture with scraps of the multilayerstructure of the present invention may be used as the polyolefin (a2)unless the object of the present invention is affected.

The melt flow rate (at 190° C., under a load of 2160 g) of thepolyolefin (a2) is preferably from 0.1 to 10 g/10 min. When the meltflow rate is included in this range, it is easy to perform coextrusionmolding and the average particle diameter of the thermoplastic resin(a1) dispersing in the adhesive resin composition (A) easily falls intoa preferred range. The melt flow rate is more preferably 0.5 g/10 min ormore, and even more preferably 1 g/10 min or more. The melt flow rate ismore preferably 5 g/10 min or less.

The adhesive resin composition (A) includes the thermoplastic resin (a1)and the polyolefin (a2). The blending weight ratio (a1/a2) of thethermoplastic resin (a1) to the polyolefin (a2) is from 1/99 to 15/85.The adhesive resin composition (A) used in the present invention canobtain satisfactory interlayer adhesion by only incorporating arelatively small amount of the thermoplastic resin (a1). A blendingweight ratio (a1/a2) of less than 1/99 will result in an insufficientinterlayer adhesion. The blending weight ratio (a1/a2) is preferably1.5/98.5 or more, and more preferably 1.75/98.25 or more. On the otherhand, a blending weight ratio (a1/a2) of greater than 15/85 will lead todeterioration of moldability and increase in production cost. Theblending weight ratio (a1/a2) is preferably 10/90 or less, and morepreferably 5/95 or less.

To the adhesive resin composition (A), antioxidants, plasticizers, heatstabilizers, UV absorbers, antistatic agents, lubricants, colorants,fillers or other resins may be added, unless the effect of the presentinvention is inhibited.

The adhesive resin composition (A) includes the thermoplastic resin (a1)and the polyolefin (a2), and it can be obtained by melt-kneading boththe materials. Although the method of melt-kneading the thermoplasticresin (a1) and the polyolefin (a2) is not particularly restricted, it isimportant to perform the melt-kneading under conditions such thatparticles of the thermoplastic resin (a1) could be dispersed at specificparticle diameters in the matrix of the polyolefin resin (a2). With sucha specific average particle diameter, a multilayer structure havingexcellent inter interlayer adhesion strength can be obtained, asdescribed in detail infra.

When a resin composition is produced by mixing a plurality of rawmaterial resins, it is generally taught that the raw material resins arepreferably mixed fully uniformly. Therefore, in most cases, mixing isconducted by using a mixing apparatus having a high mixing ability, suchas a twin-screw extruder, so that particle diameters as small aspossible could be achieved. Surprisingly, however, it has become clearthat in the adhesive resin composition (A) used in the presentinvention, the interlayer adhesion strength will rather decrease whenthe dispersed particle diameter becomes excessively small. Although thereason for this is not necessarily clear, it may be that the amount ofboron-containing functional groups which exist in the interface betweenthe layer of the adhesive resin composition (A) and the layer of theother resin (B) varies depending upon the dispersed particle diameter.When the dispersed particle diameter is excessively large, unevennessoccurs easily in the layer of the adhesive resin composition (A) and,therefore, the interlayer adhesion strength decreases also in such acase. In sum, it is very important to adjust the particle diameter ofthe thermoplastic resin (a1) in the layer of the adhesive resincomposition (A) into a specific range in order to obtain satisfactoryinterlayer adhesion strength.

Therefore, a method in which pellets of the adhesive resin composition(A) are prepared by melt-kneading the thermoplastic resin (a1) and thepolyolefin (a2), and then the resulting pellets are fed into a moldingmachine and a multilayer structure is molded is unpreferable becausekneading is performed to an excessive degree unexpectedly in many cases.It is preferred, from the interlayer adhesion point of view, tomelt-knead a thermoplastic resin (a1) and polyolefin (a2) only once inthe production of a multilayer structure. This is preferred also fromthe production cost point of view. Omission of one melt-kneadingoperation reduces the production cost of a multilayer structure. Thethermoplastic resin (a1) has highly-reactive boron-containing functionalgroups. Such functional groups, however, do not necessarily have goodmelt stability and may cause crosslinking or decomposition of a resin.As a result, a resulting multilayer structure may come to have problemssuch as decrease in interlayer adhesion strength, generation ofappearance defects, e.g., coloring, fish eyes and longitudinal streaks,and generation of odor caused by decomposition gas.

The method for molding the multilayer structure is not particularlyrestricted. For example, a method which includes coextruding theadhesive resin composition (A) and the other resin (B) or a known methodsuch as coinjection molding, extrusion coating, dry lamination andsolution coating is adopted. Among such methods, coextrusion molding andcoinjection molding are preferred. Coextrusion molding is particularlypreferred. When coextrusion is adopted, the melt-extruded components forindividual layers may be allowed to contact with each other within a dieto laminate (in-die lamination) or may be allowed to contact with eachother outside of a die to laminate (out-die lamination). If the contactis performed under pressure, the adhesion between individual layers ofthe multilayer structure can be improved. The pressure preferably rangesfrom 1 to 500 Kg/cm². In the following, description is made by takingcoextrusion molding as an example. However, it can be applied also to acase of coinjection molding instead of coextrusion molding.

In a case of coextrusion molding, a method which includes providing acoextrusion molding machine equipped with a plurality of extruders,feeding pellets of the thermoplastic resin (a1) and pellets of thepolyolefin (a2) to one extruder, feeding pellets of the resin (B) toanother extruder, and performing coextrusion molding is preferable. Inthis embodiment, it is preferable that the pellets of the thermoplasticresin (a1) and the pellets of the polyolefin (a2) be dry blended inadvance, and then fed to one extruder in a coextrusion molding machine.Although the method of the dry blending is not particularly restricted,it is preferable to fully mix pellets of the thermoplastic resin (a1)and pellets of the polyolefin (a2) mechanically in order to dry blendthem uniformly. Specific examples of a preferable method include amethod that uses a feeder which continuously weighs and mixes thepellets of the thermoplastic resin (a1) and the pellets of thepolyolefin (a2) and then feed them to an extruder continuously, and amethod in which the pellets of the thermoplastic resin (a1) and thepellets of the polyolefin (a2) are mixed by the use of a tumbler or thelike and then fed to an extruder.

In order to prevent excessive kneading, the extruder to which thepellets of the thermoplastic resin (a1) and the pellets of thepolyolefin (a2) are fed is preferably a single screw extruder. It ispreferable to melt-knead them only once in a single screw extruder andthen directly obtain a molded article. Although the constitution of thesingle screw extruder used here is not particularly limited, the L/Dthereof is usually from 5 to 50, and preferably from 10 to 50. It ispreferable to adjust the melt-kneading temperature to a temperature suchthat the resins are not degraded and their melt viscosities dropmoderately. It is preferably from 180 to 280° C., and more preferablyfrom 200 to 250° C. An excessively short residence time in the extrudermay result in failure to obtain a uniform composition, whereas anexcessively long residence time may lead to degradation of the resins.Therefore, the residence time in the extruder is preferably from 1 to 30minutes, and more preferably from 2 to 30 minutes.

In the melt-kneading in a single screw extruder, if the shear rate isexcessively high, the particle diameter of the thermoplastic resin (a1)in the resulting adhesive resin composition (A) becomes excessivelysmall, whereas if the shear rate is excessively low, the particlediameter of the thermoplastic resin (a1) in the resulting adhesive resincomposition (A) becomes excessively large. Therefore, it is important toadjust the shear rate in the melt-kneading in a single screw extruderwithin a suitable range. Specifically, the linear velocity of a screwperiphery in the single screw extruder is preferably from 0.8 to 8m/min. Here, the linear velocity (m/min) of the screw periphery is avalue which is calculated by multiplying the diameter of the screw bythe circular constant and the rate of rotation, and which is correlatedwith the shear rate in the extruder. When the linear velocity of thescrew periphery is less than 0.8 m/min, the dispersed particle diametermay become excessively large. The linear velocity is more preferably 1.2m/min or more, and even more preferably 1.5 m/min or more. On the otherhand, when the linear velocity of the screw periphery exceeds 8 m/min,the dispersed particle diameter may become excessively small. The linearvelocity is more preferably 6 m/min or less, and even more preferably 4m/min or less.

In the multilayer structure of the present invention, it is importantthat in the layer of the adhesive resin composition (A), particles ofthe thermoplastic resin (a1) are dispersed with an average particlediameter of from 0.1 to 1.2 μm in a matrix of the polyolefin (a2).Dispersion at such an average particle diameter makes it possible toobtain excellent interlayer adhesion. Here, the average particlediameter is an arithmetic average obtained by measuring the minor axesand the major axes of particles observed in a cross section of themultilayer structure produced by cutting it along the directionperpendicular to its extrusion direction (or injection direction) andaveraging them. The observation area in the layer of the adhesive resincomposition (A) is in the vicinity of the interface between the layer ofthe adhesive resin composition (A) and the layer of the resin (B).

When the average particle diameter is 0.1 μm or less, the interlayeradhesion strength decreases. The average particle diameter is preferably0.12 μm or more, and more preferably 0.14 μm or more. The interlayeradhesion strength also decreases when the average particle diameterexceeds 1.2 μm. The average particle diameter is preferably 1 μm orless, and more preferably 0.8 μm or less. Thus, it has become clear thatsatisfactory interlayer adhesion strength can be obtained when theparticle diameter is within a very limited range.

The multilayer structure of the present invention has a layer of theadhesive resin composition (A) and a layer of the resin (B). The resin(B) is not particularly restricted and examples thereof include resinssuch as polyolefins such as polyethylene (very low density, low density,middle density, high density), ethylene-vinyl acetate copolymers, EVOH,ethylene-acrylic acid ester copolymers, polypropylene,ethylene-propylene copolymers; products resulting from graftmodification of the above described polyolefins with maleic anhydride,glycidyl methacrylate, or the like; semiaromatic polyesters such as poly(ethylene terephthalate) and poly (butylene terephthalate); aliphaticpolyesters such as polyvalerolactone, polycaprolactone, poly (ethylenesuccinate) and poly (butylene succinate); aliphatic polyamides such aspolycaprolactam, polylaurolactam, polyhexamethylene adipamide andpolyhexamethylene azelamide; polyethers such as polyethylene glycol andpolyphenylene ether; polycarbonate; styrene-based polymers such aspolystyrene and styrene-acrylonitrile-butadiene copolymers; poly (methylmethacrylate); vinyl halide-based resins such as poly (vinyl chloride)and vinylidene fluoride; and the like. These resins may be used alone oralternatively may be used as a mixture of two or more of them. The resin(B) may be used as a mixture with scraps of the multilayer structure ofthe present invention unless the object of the present invention isaffected.

Among the resins provided above as examples, EVOH (B1) is particularlypreferable as the resin (B). The ethylene content of the EVOH (B1) isnot particularly limited, but it is preferably from 3 to 70 mol %. Whenthe ethylene content is less than 3 mol %, the melt stability may becomeinsufficient. The ethylene content is more preferably 5 mol % or more,and even more preferably 20 mol % or more. On the other hand, when theethylene content exceeds 70 mol %, the barrier property may becomeinsufficient. The ethylene content is more preferably 60 mol % or less,and even more preferably 50 mol % or less. The saponification degree ofthe EVOH (B1) is usually from 10 to 100 mol %, preferably from 50 to 100mol %, more preferably from 80 to 100 mol %, even more preferably from95 to 100 mol %, and most preferably from 99 to 100 mol %. When thesaponification degree is low, the degree of crystallinity of the EVOH(B1) may become insufficient or the thermal stability duringmelt-forming may become insufficient.

The EVOH (B1) can be prepared by a known method including copolymerizingethylene and a vinyl ester using a radical initiator and thensaponifying the resulting copolymer in the presence of an alkalinecatalyst. Examples of the vinyl ester include vinyl acetate, vinylpropionate, vinyl pivalate, vinyl caprate, vinyl benzoate, and the like.Among such vinyl esters, only one ester may be used and two or moreesters may also be used in combination. Among these, vinyl acetate ispreferred.

Unless the object of the present invention is disturbed,copolymerization may be performed in the presence of othercopolymerizable components. The other components include olefin-basedmonomers such as propylene, 1-butene and isobutene; acrylamide-basedmonomers such as acrylamide, N-methylacrylamide, N-ethylacrylamide andN,N-dimethylacrylamide; methacrylamide-based monomers such asmethacrylamide, N-methylmethacrylamide, N-ethylacrylamide andN,N-dimethylmethacrylamide; vinyl ether-based monomers such as methylvinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinylether, tert-butyl vinyl ether and dodecyl vinyl ether; allyl alcohol;vinyltrimetoxysilane; N-vinyl-2-pyrrolidone; and the like.

The EVOH (B1) obtained in such a manner may be used alone or may be usedin combination with another EVOH (B1) different in ethylene content,saponification degree, polymerization degree, or the like. Further,unless the object of the present invention is disturbed, it may be usedwith addition of thermoplastic resins other than the EVOH (B1). Thecontent of the thermoplastic resins in the EVOH (B1) preferably fallswithin the range of from 0 to 50% by weight, more preferably within therange of from 0 to 40% by weight, and even more preferably within therange of from 0 to 10% by weight.

A preferable layer constitution of the multilayer structure is aconstitution in which the layer of the EVOH (B1) and a layer of ahydrophobic thermoplastic resin are laminated to each other via thelayer of the adhesive resin composition (A). This a composition whichcompensates drawbacks of EVOH (B1), namely, high moisture permeabilityand high expense. Examples of such hydrophobic thermoplastic resinsinclude polyolefin (B2), styrene-based polymers, polyesters, and thelike. A particularly preferable embodiment is one in which a layer ofthe ethylene-vinyl alcohol copolymer (B1) and a layer of a polyolefin(B2) are laminated to each other via the layer of the adhesive resincomposition (A).

Preferable examples of the layer constituting the multilayer structureof the present invention include those shown below. Here, A, B1, B2, andReg represent an adhesive resin composition, an EVOH, a hydrophobicthermoplastic resin typified by polyolefin, and a resin layer containinga scrap of a multilayer structure, respectively. The B2 may contain aplurality of layers. The thicknesses of the individual layers of themultilayer structure may optionally be selected. Such selection allowsthe total thickness of the multilayer structure to fall within a desiredrange.

2 layers: A/B1

3 layers: B1/A/B2

4 layers: B1/A/Reg/B2

5 layers: B2/A/B1/A/B2, B2/A/B1/A/Reg, B1/A/B2/Reg/B2

6 layers: B2/Reg/A/B1/A/B2

7 layers: B2/Reg/A/B1/A/Reg/B2

The multilayer structure obtained in such a manner is excellent ininterlayer adhesion as being clear from the Examples shown infra. Evenwhen it is recovered and reused, less appearance abnormalities, such asdisturbance in a surface, gels and hard spots, will be generated. Themultilayer structure can be subjected further to, for example,stretching operations such as uniaxially stretching, biaxial stretchingand blow stretching, and thermoforming operations such asvacuum/pressure molding. It can also be fabricated into molded articles,such as films, sheets, bottles and cups, excellent in dynamic propertiesand gas barrier properties. The molded articles obtained are useful forapplications where a gas barrier property is required such as materialsfor wrapping foods, materials for wrapping medical items (drugs andmedical appliances) and fuel tanks.

EXAMPLE

The present invention will be described in more detail below by way ofExamples, to which, however, the present invention is not limited atall. In the following description, a ratio means a weight ratio and “%”means “% by weight” unless otherwise stated. The average particlediameter of thermoplastic resin (a1) was measured by the followingmethod.

Method of Average Particle Diameter Measurement

The structure of a layer of an adhesive resin composition (A) wasobserved by cutting a multilayer sheet along the direction perpendicularto the direction of extrusion, and photographing a cross section of thelayer of the adhesive resin composition (A) at a magnification of 30,000using a transmission electron microscope. A threshold value at whichmajor particles could be recognized as particles and the backgroundwould not be continued in black was set and the photographed image wasconverted into binary (black-and-white) image. In the binary image,major axes and minor axes of all particles contained in a square area of1.6 μm×1.6 μm containing the interface between the layer of the adhesiveresin composition (A) and the layer of the EVOH (B1) as one side of thesquare were measured and the average of all the measurements was definedas the average particle diameter. In this measurement, dots as small as0.0005 μm or less, which could not be distinguished from the shade ofthe image, were omitted from the objects of the measurement.

Synthesis Example 1 Synthesis of Boronic Acid Ester Group-ContainingSEBS (X-1)

A styrene-hydrogenated butadiene-styrene block copolymer (SEBS,styrene/hydrogenated butadiene=16/84 (weight ratio), hydrogenationpercentage of butadiene units=94%, amount of double bonds=960 μeq/g,melt flow rate=5 g/10 min (at 230° C., under a load of 2160 g) was fedto a twin-screw extruder at a rate of 7 kg/hr while ventilating the feedport with 1 L/min nitrogen. Subsequently, while feeding a mixed solutionof borane-triethylamine complex (TEAB) and boronic acid 1,3-butanediolester (BBD) (TEAB/BBD=29/71 (weight ratio)) from a liquid feeder 1 at arate of 0.6 kg/hr and 1,3-butanediol from a liquid feeder 2 at a rate of0.4 kg/hr, melt-kneading was carried out continuously. During thekneading, the pressure was regulated so that the gauges at a vent 1 anda vent 2 indicated about 20 mmHg. As the result, SEBS (X-1) containingboronic acid 1,3-butanediol ester groups (BBDE) was obtained from thedischarge port at a rate of 7 kg/hr. The SEBS contained boronic acid1,3-butanediol ester groups in an amount of 650 μeq/g and double bondsin an amount of 115 μeq/g, and had a melt flow rate of 1.6 g/10 min (at190° C., under a load of 2160 g).

The constitution and operating conditions of the twin-screw extruderused for the reaction are as follows:

Co-rotating twin-screw extruder TEM-35B (manufactured by Toshiba MachineCo., Ltd.)

Screw diameter: 37 mmφ

L/D: 52 (15 blocks)

Liquid feeder: C3 (Liquid feeder 1), C11 (Liquid feeder 2)

Vent position: C6 (Vent 1), C14 (Vent 2)

Constitution of screw: Seal rings were used between C5 and C6, betweenC10 and C11, and at C12.

Preset cylinder temperature: C1 (water cooling), C2-C3 (200° C.), C4-C15(250° C.), die (250° C.)

Screw speed: 400 rpm

Synthesis Example 2 Synthesis of Boronic Acid Ester Group-ContainingSEBS (X-2)

SEBS (X-2) containing boronic acid 1,3-butanediol ester groups (BBDE)was synthesized in the same manner as in Synthesis Example 1, except forusing a styrene-hydrogenated butadiene-styrene block copolymer(styrene/hydrogenated butadiene=16/84 (weight ratio), hydrogenationpercentage of butadiene units=94%, amount of double bonds=960 μeq/g,melt flow rate=3 g/10 min (at 230° C., under a load of 2160 g). The SEBS(X-2) contained boronic acid 1,3-butanediol ester groups in an amount of650 μeq/g and double bonds in an amount of 115 μeq/g, and had a meltflow rate of 0.6 g/10 min (at 190° C., under a load of 2160 g).

Example 1

Pellets of SEBS (X-1) obtained in Synthesis Example 1 and pellets oflinear low-density polyethylene (LLDPE) “ULTZEX 2022L” produced byMitsui Chemicals, Inc. (melt flow rate=2.1 g/10 min (at 190° C., under aload of 2160 g), density=0.919 g/cm³) were dry-blended at a weight ratioof 4/96 by use of a tumbler, yielding a mixture of both pellets.

Next, high-density polyethylene (HDPE) “LF443” produced by JapanPolyethylene Corporation (melt flow rate=1.5 g/10 min (at 190° C., undera load of 2160 g), the pellet mixture, and EVOH “F171B” produced byKuraray Co., Ltd. (ethylene content=32 mol %) were provided as rawmaterials and were introduced into separate extruders, respectively.Then, a 3-kind 5-layer multilayer sheet of HDPE/adhesive resincomposition (A)/EVOH/adhesive resin composition (A)/HDPE was produced bycoextrusion molding according to the conditions shown below. Thethickness distribution of the resulting multilayer sheet was50/10/10/10/50 μm.

The constitution and operating conditions of the coextrusion moldingmachine are as follows.

Extruder 1 [HDPE (B2)]:

Instrument: single screw extruder “GT-32-A type” produced by PLABOR Co.,Ltd.

Screw diameter: 32 mmφ

Screw speed: 62 rpm

Preset cylinder temperature: 220° C.

Extruder 2 [adhesive resin composition (A)]:

Instrument: single screw extruder “P25-18AC” manufactured by Osaka SeikiKosaku

Screw diameter: 25 mmφ

Screw constitution: fullflight

L/D: 18

Screw speed: 30 rpm

Linear velocity of screw periphery: 2.36 m/min

Preset cylinder temperature: 220° C.

Discharge rate: about 1 kg/hr

Residence time in extruder: about 9 min

Residence time in die: about 2 min

Extruder 3 [EVOH (B1)]:

Instrument: single screw extruder “Labo ME-type CO-NXT” produced by ToyoSeiki Seisaku-sho, Ltd.

Screw diameter: 20 mmφ

Screw speed: 18 rpm

Preset cylinder temperature: 220° C.

Die size: 300 mm

Sheet taking-off rate: 4 m/min

Temperature of cooling roll: 50° C.

The T-type peel strength in the interface between the adhesive resincomposition (A) layer and the EVOH (B1) layer of the resultingmultilayer sheet immediately after the sheet production was measuredwith an Autograph (tensile speed=250 mm/min) at 20° C. and 65% RH. Theobtained value was defined as an interlayer adhesion. The interlayeradhesion was 1650 g/15 mm. Moreover, the structure of the adhesive resincomposition (A) layer was observed by cutting the multilayer sheet alongthe direction perpendicular to the direction of extrusion, andphotographing a cross section of the adhesive resin composition (A)layer at a magnification of 30,000 using a transmission electronmicroscope. In the adhesive resin composition (A) layer, particles ofSEBS (X-1) were dispersed in a matrix of LLDPE. The measurement of theaverage particle diameter of the thermoplastic resin (a1) by the methodpreviously described revealed that the average particle diameter was 0.2μm.

Example 2

A multilayer structure was obtained in the same manner as in Example 1,except for using SEBS (X-2) obtained in Synthesis Example 2 instead ofSEBS (X-1) in Example 1. The results evaluated in the same manner as inExample 1 are shown in Table 1.

Example 3

In Example 1, the rotation rate of the extruder 2 to which the adhesiveresin composition (A) was introduced was increased to 1.6 times (48 rpm)and the linear velocity of the screw periphery was adjusted to 3.77m/min. At this time, the rotation rates of the extruders 1 and 2 werealso increased to 1.6 times, and the sheet taking-off rate was alsoincreased to 1.6 times. A multilayer sheet having the same thickness asin Example 1 was obtained in the same manner as in Example 1 except forthese points. The results evaluated in the same manner as in Example 1are shown in Table 1.

Example 4

A multilayer sheet was obtained in the same manner as in Example 1except for using low density polyethylene (LDPE) produced by Asahi KaseiChemicals Corporation, “Suntec L2340” (melt flow rate 3.8 g/10 minmeasured at 190° C., under a load of 2160 g, and a density of 0.923g/cm³) instead of linear low density polyethylene (LLDPE) to be dryblended in Example 1. The results evaluated in the same manner as inExample 1 are shown in Table 1.

Example 5

A multilayer sheet was obtained in the same manner as in Example 1except for using ethylene-vinyl acetate copolymer resin (EVAc) “EV360”(melt flowrate 2.0 g/10 min at 190° C., under a load of 2160 g, and adensity of 0.950 g/cm³) produced by Du Pont-Mitsui Polychemicals Co.,Ltd., instead of linear low density polyethylene (LLDPE) to be dryblended in Example 1. The results evaluated in the same manner as inExample 1 are shown in Table 1.

Example 6

A multilayer sheet was obtained in the same manner as in Example 1except for using polypropylene (PP) “EG7F” (melt flow rate 1.3 g/10 minat 190° C., under a load of 2160 g) produced by Japan PolypropyleneCorporation instead of linear low density polyethylene (LLDPE) to bedisposed as an outer layer of the multilayer sheet in Example 1. Theresults evaluated in the same manner as in Example 1 are shown in Table1.

Example 7

A multilayer sheet was obtained in the same manner as in Example 1,except for changing the blending weight of SEBS (X-1) to linear lowdensity polyethylene (LLDPE) in Example 1 to 2/98. The results evaluatedin the same manner as in Example 1 are shown in Table 1.

Comparative Example 1

A multilayer sheet was obtained in the same manner as in Example 1,except for introducing pellets of a resin composition obtained bymelt-kneading in a twin-screw extruder beforehand instead of introducingthe mixture of the pellets into the extruder 2 in Example 1. The resultsevaluated in the same manner as in Example 1 are shown in Table 1. Theconstruction and driving conditions of the twin-screw extruder used forthe melt-kneading are as follows:

Co-rotating twin-screw extruder Labo Plastomil (manufactured by ToyoSeiki Seisaky-sho Co., Ltd.)

Screw construction: Co-rotation twin-screw

Screw diameter: 25 mmφ

L/D: 25

Preset cylinder temperature: 220° C.

Screw speed: 150 rpm

Linear velocity of screw periphery: 11.78 m/min

Rate of feeding of resin: 5 kg/hr

Residence time: 2 minutes

Comparative Example 2

A multilayer sheet was obtained in the same manner as in Example 1,except for changing the blending weight of SEBS (X-1) to linear lowdensity polyethylene (LLDPE) to 0.5/99.5. The results evaluated in thesame manner as in Example 1 are shown in Table 1.

Comparative Example 3

In Example 1, the rotation rate of the extruder 2 to which the adhesiveresin composition (A) was increased to 3.73 times (112 rpm) and thelinear velocity of the screw periphery was adjusted to 8.80 m/min. Atthis time, the rotation rate of the extruder 1 was increased to 1.87times and the rotation rate of the extruder 2 was increased to 3.73times. The sheet taking-off rate was increased to 3.73 times. A 3-kind,5-layer multilayer sheet in which HDPE/adhesive resin composition(A)/EVOH/adhesive resin composition (A)/HDPE=25/10/10/10/25 μm wasproduced by coextrusion molding in the same manner as in Example 1except for these points. The resulting multilayer sheet was evaluated inthe same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 4

In Example 1, the rotation rate of the extruder 2 to which the adhesiveresin composition (A) was decreased to 0.33 times (10 rpm) and thelinear velocity of the screw periphery was adjusted to 0.79 m/min. Atthis time, the rotation rates of the extruders 1 and 2 were alsodecreased to 0.33 times, and the sheet taking-off rate was alsodecreased to 0.33 times. A multilayer sheet having the same thickness asin Example 1 was obtained in the same manner as in Example 1 except forthese points. The results evaluated in the same manner as in Example 1are shown in Table 1.

Comparative Example 5

A multilayer sheet was obtained in the same manner as ComparativeExample 1 except for using low density polyethylene (LDPE) “SuntecL2340” (melt flow rate 3.8 g/10 min at 190° C., under a load of 2160 g,and a density of 0.923 g/cm³) produced by Asahi Kasei ChemicalsCorporation instead of linear low density polyethylene (LLDPE) to bemelt-kneaded in Comparative Example 1. The results evaluated in the samemanner as in Example 1 are shown in Table 1.

Comparative Example 6

A multilayer sheet was obtained in the same manner as ComparativeExample 1 except for using ethylene-vinyl acetate copolymer resin (EVAc)“EV360” (melt flow rate 2.0 g/10 min at 190° C., under a load of 2160 g,and a density of 0.950 g/cm³) produced by Du Pont-Mitsui PolychemicalsCo., Ltd., instead of linear low density polyethylene (LLDPE) to bemelt-kneaded in Comparative Example 1. The results evaluated in the samemanner as in Example 1 are shown in Table 1.

Comparative Example 7

A multilayer sheet was obtained in the same manner as in ComparativeExample 1 except for using polypropylene (PP) “EG7F” (melt flow rate 1.3g/10 min at 190° C., under a load of 2160 g) produced by JapanPolypropylene Corporation instead of linear low density polyethylene(LLDPE) to be disposed as an outer layer of the multilayer sheet inComparative Example 1. The results evaluated in the same manner as inExample 1 are shown in Table 1.

Example 8

Pellets of SEBS (X-1) obtained in Synthesis Example 1 and pellets oflow-density polyethylene (LDPE) “MIRASON 102” produced by MitsuiChemicals, Inc. (melt flow rate 0.35 g/10 min at 190° C., under a loadof 2160 g, and a density of 0.919 g/cm³) were dry-blended at a weightratio of 10/90 by use of a tumbler, yielding a mixture of both pellets.

A 3-kind, 5-layer multilayer direct blown bottle in which LDPE/adhesiveresin composition (A)/EVOH/adhesive resin composition (A)/LDPE (averagethickness at a body part of the direct blown bottle: 340/40/40/40/340μm) was produced by using low density polyethylene (LDPE) “MIRASON 102”produced by Mitsui Chemicals, Inc. (melt flow rate 0.35 g/10 min at 190°C., under a load of 2160 g), the aforementioned pellet mixture, and EVOH“F171B” (ethylene content 32 mol %) produced by Kuraray Co., Ltd. as rawmaterials, and using a 4-kind, 7-layer blow molding machine “TB-ST-6P”manufactured by Suzuki Tekkosho Co. At this time, the extrudertemperature for LDPE was 220° C. The extruder temperature of theadhesive resin composition (A) was 210° C. The extruder temperature forEVOH was 210° C. The resin temperature in the die was 220° C. The dietemperature was 40° C. The average particle diameter as measured in thesame manner as in Example 1 was 0.5 μm. Water was filled as content intothe resulting direct blown bottle, which was then sealed tightly undernormal pressure. Then, while the bottle was kept with its bodyhorizontal, it was allowed to fall freely from a height of 50 cm to a90°-angled edge of triangular pole having 20 cm in lengths so that theedge could hit the center of the bottle body. However, no interlayerdelamination generated and it was confirmed that a performance meetingrequirements can be obtained.

The constitution and driving conditions of the extruder used for moldingare as follows:

Instrument: 4-kind, 7-layer direct blow molding machine manufactured bySuzuki Tekkosho Co.

Single screw extruder 1 (HDPE):

Screw diameter: 45 mmφ,

Screw speed: 20 rpm

Preset cylinder temperature: 200° C.

Single screw extruder 2 (HDPE):

Screw diameter: 40 mmφ,

Screw speed: 17 rpm

Preset cylinder temperature: 200° C.

Single screw extruder 3 (adhesive resin composition (A))

Screw diameter: 35 mmφ

Screw constitution: fullflight

L/D: 23

Screw speed: 11 rpm

Preset cylinder temperature: 200° C.

Discharge rate: about 0.7 kg/hr

Residence time in extruder: about 10 min

Single screw extruder 4 (EVOH):

Screw diameter: 35 mmφ

Screw speed: 5.3 rpm

Preset cylinder temperature: 210° C.

TABLE 1 Adhesive resin composition (A) Linear Thermoplastic velocity ofAverage Interlayer resin (a1) Polyolefin (a2) Weight screw particleadhesion MFR MFR ratio Blending periphery Layer diameter strength Kind(g/10 min) Kind (g/10 min) (a1/a2) method (m/min) constitution^(*2))(μm) (g/15 mm) Example 1 SEBS 1.6 LLDPE 2.1 4/96 Dry 2.36 A 0.2 1650Example 2 SEBS 0.6 LLDPE 2.1 4/96 Dry 2.36 A 0.4 1400 Example 3 SEBS 1.6LLDPE 2.1 4/96 Dry 3.77 A 0.2 1600 Example 4 SEBS 1.6 LDPE 3.8 4/96 Dry2.36 A 0.2 1480 Example 5 SEBS 1.6 EVAc 2 4/96 Dry 2.36 A 0.25 1700Example 6 SEBS 1.6 LLDPE 2.1 4/96 Dry 2.36 C 0.2 1620 Example 7 SEBS 1.6LLDPE 2.1 2/98 Dry 2.36 A 0.2 1530 Comparative SEBS 1.6 LLDPE 2.1 4/96Melt 11.78/2.36^(*1)) A 0.06 1200 Example 1 Comparative SEBS 1.6 LLDPE2.1 0.5/99.5 Dry 2.36 A 0.1 100 Example 2 Comparative SEBS 1.6 LLDPE 2.14/96 Dry 8.8  B 0.05 900 Example 3 Comparative SEBS 1.6 LLDPE 2.1 4/96Dry 0.79 A 1.4 850 Example 4 Comparative SEBS 1.6 LDPE 3.8 4/96 Melt11.78/2.36^(*1)) A 0.05 1050 Example 5 Comparative SEBS 1.6 EVAc 2 4/96Melt 11.78/2.36^(*1)) A 0.04 1020 Example 6 Comparative SEBS 1.6 LLDPE2.1 4/96 Melt 11.78/2.36^(*1)) C 0.05 1130 Example 7 *¹⁾Peripherallinear velocity in the pellet production/peripheral linear velocity inthe molding *²⁾A: HDPE/adhesive resin composition (A)/EVOH/adhesiveresin composition (A)/HDPE = 50/10/10/10/50 (μm) B: HDPE/adhesive resincomposition (A)/EVOH/adhesive resin composition (A)/HDPE =25/10/10/10/25 (μm) C: PP/adhesive resin composition (A)/EVOH/adhesiveresin composition (A)/PP = 50/10/10/10/50 (μm)

As is clear from Table 1, in Examples 1 to 7 where the average particlediameter of the thermoplastic resin (a1) is in the range of from 0.1 to1.2 μm, satisfactory interlayer adhesion strengths have been obtained.Conversely, in Comparative Examples 1, 5, 6 and 7 where pellets of theadhesive resin composition (A) were produced by melt-kneading in a twinscrew extruder beforehand, and then molding was conducted, the averageparticle diameter became less than 0.1 μm, resulting in greatlydecreased interlayer adhesion strengths. Also in Comparative Example 3where the linear velocity of the screw periphery of the extruder ishigh, the average particle diameter became less than 0.1 μm, resultingin greatly decreased interlayer adhesion strength. On the other hand, inComparative Example 4 where the linear velocity of the screw peripheryof the extruder is low, the average particle diameter became over 1.2μm, also resulting in a greatly decreased interlayer adhesion strength.That is, the interlayer adhesion strength decreases greatly in bothcases where the average particle diameter of the thermoplastic resin(a1) is excessively large or excessively small, and it therefore havebecome clear that the interlayer adhesion strength becomes satisfactorywhen the thermoplastic resin (a1) has a specific average particlediameter. The interlayer adhesion strength in Example 7 where theblending weight ratio (a1/a2) of the thermoplastic resin (a1) to thepolyolefin (a2) is 2/98 is 1530 g/15 mm and it is slightly less than theinterlayer adhesion strength (1650 g/15 mm) in Example 1 where theblending weight ratio (a1/a2) is 4/96. Conversely, in ComparativeExample 2 where the blending weight ratio (a1/a2) is 0.5/99.5, theinterlayer adhesion strength is only 100 g/15 mm, and it is shown thatthe interlayer adhesion strength has decreased greatly. That is, it isshown that the interlayer adhesion strength changes sharply between ablending weight ratio (a1/a2) of 0.5/99.5 and that of 2/98 and theinterlayer adhesion strength is increased by blending only a smallamount of the thermoplastic resin (a1).

1. A multilayer structure comprising a layer of an adhesive resincomposition (A) and a layer of an ethylene-vinyl alcohol copolymer (B1),wherein the adhesive resin composition (A) comprises a thermoplasticresin (a1) containing functional groups of at least one selected fromthe group consisting of a boronic acid group and a boron-containinggroup capable of being converted into a boronic acid group in thepresence of water, and a polyolefin (a2) which does not contain thefunctional groups, the blending weight ratio (a1/a2) of thethermoplastic resin (a1) to the polyolefin (a2) is 1/99 to 15/85, andparticles of the thermoplastic resin (a1) are dispersed with an averageparticle diameter of 0.1 to 1.2 μm in a matrix of the polyolefin (a2).2. The multilayer structure according to claim 1, wherein the melt flowrate, at 190° C. under a load of 2160 g, of the thermoplastic resin (a1)is from 0.7 to 4 g/10 min.
 3. The multilayer structure according toclaim 1, wherein the melt flow rate, at 190° C. under a load of 2160 g,of the polyolefin (a2) is from 0.1 to 10 g/10 min.
 4. The multilayerstructure according to claim 1, wherein a layer of the ethylene-vinylalcohol copolymer (B1) and a layer of a polyolefin (B2) are laminated toeach other via the layer of the adhesive resin composition (A).
 5. Amethod for producing the multilayer structure according to claim 1,comprising providing a coextrusion molding machine equipped with aplurality of extruders, feeding pellets of the thermoplastic resin (a1)and pellets of the polyolefin (a2) to one extruder, feeding pellets ofthe resin (B) to another extruder, and performing coextrusion molding.6. The method for producing a multilayer structure according to claim 5,wherein the pellets of the thermoplastic resin (a1) and the pellets ofthe polyolefin (a2) are dry blended in advance, and then fed to theextruder.
 7. The method for producing a multilayer structure accordingto claim 5, wherein the extruder to which the pellets of thethermoplastic resin (a1) and the pellets of the polyolefin (a2) are fedis a single screw extruder.
 8. The method for producing a multilayerstructure according to claim 7, wherein the linear velocity of a screwperiphery in the single screw extruder is from 0.8 to 8 m/min.
 9. Themethod for producing a multilayer structure according to claim 6,wherein the extruder to which the pellets of the thermoplastic resin(a1) and the pellets of the polyolefin (a2) are fed is a single screwextruder.
 10. The method for producing a multilayer structure accordingto claim 9, wherein the linear velocity of a screw periphery in thesingle screw extruder is from 0.8 to 8 m/min.
 11. The multilayerstructure according to claim 1, wherein the adhesive resin composition(A) consists of the thermoplastic resin (a1) and the polyolefin (a2).12. The multilayer structure according to claim 1, wherein theboron-containing group is a functional group selected from the groupconsisting of a compound of formula (II), a compound of formula (III),and a compound of formula (IV):

wherein X₁ and X₂ are the same or different and each represent ahydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbongroup, or an aromatic hydrocarbon group, where the aliphatic hydrocarbongroup, the alicyclic hydrocarbon group and the aromatic hydrocarbongroup may have a substituent, X₁ and X₂ may be combined together,provided that in no cases both X₁ and X₂ are hydrogen atoms; R₁, R₂ andR₃ each represent a hydrogen atom, an aliphatic hydrocarbon group, analicyclic hydrocarbon group or an aromatic hydrocarbon group, where thealiphatic hydrocarbon group, the alicyclic hydrocarbon group and thearomatic hydrocarbon group may have a substituent; and M representsalkali metal.